Special Issue "Gene Expression Regulation during Drought and Salt Stress in Crop Plants"

A special issue of Agronomy (ISSN 2073-4395).

Deadline for manuscript submissions: 15 April 2019

Special Issue Editor

Guest Editor
Dr. Andrew Eamens

Centre for Plant Science, School of Environmental and Life Sciences, University of Newcastle, Callaghan, New South Wales, 2308, Australia
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Special Issue Information

Dear Colleagues,

The world population is expanding more rapidly than ever before; however, the area of arable land either available to, or remaining useable for, cropping agriculture is decreasing at an alarming rate. Further, our ability to continue to improve total crop yield via the use of traditional methods is also hastily-approaching transition from the once impressive exponential phase to plateauing out in the stationary phase of the production curve for global crop yield.

Two closely-linked abiotic stresses, drought and salt stress, are of increasing concern for modern agriculture to continue to achieve annual improvements to total crop yield and therefore, meet our food security target. A tremendous volume of research effort has been spent in recent years by the plant biology research community to; (1) advance our current understand of the mechanisms employed by plants to mount an adaptive response to drought or salt stress, and; (2) translate research findings made in experimental model plant species into the major crop species, including rice, wheat, maize, barley and soybean, to provide tolerance to these two stresses.

Much of the knowledge gained, or the research translated into crops species to date, has focused on the regulation of the expression genes that encode the protein products key to the biochemical or physiological pathways responsible for providing tolerance to drought or salt stress. We also now know that the regulation of gene expression is far more complex than previously thought, with the ‘central dogma’ of molecular genetics, that is; from DNA template, to RNA intermediate, to protein product, being challenged on an increasingly frequent basis.

This Special Issue of Agronomy, titled “Gene Expression Regulation during Drought and Salt Stress in Crop Plants” will focus on the recent advances made by the plant biology research community on the complexity of the regulation of expression key genes involved in a crop plant’s response to drought or salt stress. We, therefore, warmly welcome novel research findings, review articles and opinion pieces covering the broad, yet related areas of; epigenetics (including chromatin modification and DNA methylation); genetic diversity (including natural variation); alterations to transcription factor expression; small RNA-directed RNA silencing (including the microRNA and small-interfering RNA species), and; the use of a transgene-based approach to molecularly manipulate gene expression in crop species to provide tolerance to either drought or salt stress (including the in planta application of the new sequence-specific nuclease toolkit for targeted mutagenesis).

Dr. Andrew Eamens
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Agronomy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Stress tolerance
  • Genetic diversity
  • Natural variation
  • Transcription factors
  • DNA methylation
  • Epigenetics
  • microRNAs
  • small-interfering RNAs
  • Sequence-specific nucleases
  • in planta molecular manipulation.

Published Papers (7 papers)

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Research

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Open AccessArticle Unveiling the Enigmatic Structure of TdCMO Transcripts in Durum Wheat
Agronomy 2018, 8(11), 270; https://doi.org/10.3390/agronomy8110270 (registering DOI)
Received: 2 October 2018 / Revised: 7 November 2018 / Accepted: 19 November 2018 / Published: 21 November 2018
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Abstract
Durum wheat is one of the oldest and most important edible cereal crops and its cultivation has considerable economic importance in many countries. However, adverse conditions, such as high irradiance and increasing salinity of soils, could lead to a decrease in productivity over
[...] Read more.
Durum wheat is one of the oldest and most important edible cereal crops and its cultivation has considerable economic importance in many countries. However, adverse conditions, such as high irradiance and increasing salinity of soils, could lead to a decrease in productivity over the next few decades. Durum wheat plants under salinityare able toaccumulate glycine betaine to osmotically balance the cytosol and reduce oxidative stress, especially in young tissues. However, the synthesis of this fundamental osmolyte is inhibited by high light in T. durum even under salinity. Choline monooxygenase is the first enzyme involved in the glycine betaine biosynthetic pathway. Thus, to explain the glycine betaine inhibition, we analyzed the effect of both salinity and high light on the putative TdCMO gene expression. Thirty-eight TdCMO different transcripts were isolated in the young leaves of durum wheat grown in different stress conditions. All translated amino acid sequences, except for the TdCMO1a6 clone, showed a frame shift caused by insertions or deletions. The presence of different transcripts could depend on the presence of duplicated genes, different allelic forms, and alternative splicing events. TdCMO1a6 computational modeling of the 3D structure showed that in durum wheat, a putative CMO-like enzyme with a different Rieske type motif, is present and could be responsible for the glycine betaine synthesis. Full article
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Open AccessArticle Characterization for Drought Tolerance and Physiological Efficiency in Novel Cytoplasmic Male Sterile Sources of Sunflower (Helianthus annuus L.)
Agronomy 2018, 8(10), 232; https://doi.org/10.3390/agronomy8100232
Received: 11 September 2018 / Revised: 11 October 2018 / Accepted: 17 October 2018 / Published: 19 October 2018
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Abstract
Sunflower is sensitive to drought, and furthermore, sunflower hybrids display limited cytoplasmic diversity. In addition, the wild cytoplasmic sources of sunflower are not well explored for their potential to introduce drought tolerance into newly developed hybrids. Therefore here, we carried out a Line
[...] Read more.
Sunflower is sensitive to drought, and furthermore, sunflower hybrids display limited cytoplasmic diversity. In addition, the wild cytoplasmic sources of sunflower are not well explored for their potential to introduce drought tolerance into newly developed hybrids. Therefore here, we carried out a Line × Tester-based genetic study using 19 sunflower genotypes representing, 13 cytoplasmic male sterile (CMS) lines from wild and conventional sources, 2 maintainer lines, and 4 restorer lines. The CMS and maintainer lines were crossed with restorer lines to develop sixty F1 hybrids. The parents and their hybrids were evaluated under two water regimes, normal irrigation and drought stress (i.e., withholding water). A total of twelve important plant descriptors were studied over a period of two years and the significant differences between parents and hybrids are reported here. More specifically, hybrid lines were higher in average values for all the descriptors. The contribution of female parent was more prominent in the expression of traits in hybrids as compared to male parents. The CMS sources varied significantly regarding seed yield per plant and other physiological traits. Proline content in the leaves of all the genotypes was three times higher in the water stress regime. Accession CMS-PKU-2A was identified as the best general combiner for leaf area and specific leaf weight., whereas CMS-234A was the best general combiner for biological yield and photosynthetic efficiency under both conditions. The cross combinations CMS-ARG-2A × RCR-8297, CMS-234A × P124R, and CMS-38A × P124R were found significant for biological yield, seed yield and oil content under both environments. Overall, this study provides useful information about the cytoplasmic effects on important sunflower traits and drought stress tolerance. Full article
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Open AccessArticle Screening of EMS-Induced Drought-Tolerant Sugarcane Mutants Employing Physiological, Molecular and Enzymatic Approaches
Agronomy 2018, 8(10), 226; https://doi.org/10.3390/agronomy8100226
Received: 3 September 2018 / Revised: 7 October 2018 / Accepted: 11 October 2018 / Published: 15 October 2018
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Abstract
Drought stress is one of the major agronomic concerns that lead towards a sharp decline in sugarcane yield. An urgent demand to overcome drought is critical to ensure sugarcane production. Mutation breeding is one of the promising tools available to produce stress-resistant plants,
[...] Read more.
Drought stress is one of the major agronomic concerns that lead towards a sharp decline in sugarcane yield. An urgent demand to overcome drought is critical to ensure sugarcane production. Mutation breeding is one of the promising tools available to produce stress-resistant plants, with the induction of new alleles due to point mutation within existing sugarcane germplasm. The current study was directed to chemically mutagenize the calli of two sugarcane cultivars (ROC22 and FN39) via 0.1% EMS, with focus on inducing mutations in their genome. The 1644 regenerated plants of ROC22 and 1398 of FN39 were exposed to 28% PEG-6000 stimulated osmotic stress. Eighteen plants of ROC22 and 2 plants of FN39, that survived after in vitro osmotic stress treatment, were then subjected to preliminary greenhouse pot trials to confirm drought tolerance by analyzing them using various physiological parameters, including photosystem II (PSII) photochemical efficiency (Fv/Fm), leaf chlorophyll content, and photosynthetic rate. The genetic diversity among drought-resistant mutant lines was further assessed by 15 pairs of simple sequence repeat (SSR) markers amplification and CEL (Celery) I endonuclease digestion, to investigate the mutated sites. Mutant lines of ROC22 (i.e., MR22-15 and MR22-20) were found to be promising for future drought resistance breeding, due to better physiological adaptation under drought stress. Full article
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Open AccessArticle Chitosan-PVA and Copper Nanoparticles Improve Growth and Overexpress the SOD and JA Genes in Tomato Plants under Salt Stress
Agronomy 2018, 8(9), 175; https://doi.org/10.3390/agronomy8090175
Received: 3 August 2018 / Revised: 22 August 2018 / Accepted: 6 September 2018 / Published: 8 September 2018
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Abstract
Saline stress severely affects the growth and productivity of plants. The activation of hormonal signaling cascades and reactive oxygen species (ROS) in response to salt stress are important for cellular detoxification. Jasmonic acid (JA) and the enzyme SOD (superoxide dismutase), are well recognized
[...] Read more.
Saline stress severely affects the growth and productivity of plants. The activation of hormonal signaling cascades and reactive oxygen species (ROS) in response to salt stress are important for cellular detoxification. Jasmonic acid (JA) and the enzyme SOD (superoxide dismutase), are well recognized markers of salt stress in plants. In this study, the application of chitosan-polyvinyl alcohol hydrogels (Cs-PVA) and copper nanoparticles (Cu NPs) on the growth and expression of defense genes in tomato plants under salt stress was evaluated. Our results demonstrate that Cs-PVA and Cs-PVA + Cu NPs enhance plant growth and also promote the expression of JA and SOD genes in tomato (Solanum lycopersicum L.), under salt stress. We propose that Cs-PVA and Cs-PVA + Cu NPs mitigate saline stress through the regulation of oxidative and ionic stress. Full article
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Open AccessArticle Assessing Field Prunus Genotypes for Drought Responsive Potential by Carbon Isotope Discrimination and Promoter Analysis
Received: 27 February 2018 / Revised: 2 April 2018 / Accepted: 4 April 2018 / Published: 5 April 2018
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Abstract
In order to improve the effectiveness of breeding practices for Prunus rootstocks, it is essential to obtain new resistance resources, especially with regard to drought. In this study, a collection of field-grown Prunus genotypes, both wild-relative species and cultivated hybrid rootstocks, were subjected
[...] Read more.
In order to improve the effectiveness of breeding practices for Prunus rootstocks, it is essential to obtain new resistance resources, especially with regard to drought. In this study, a collection of field-grown Prunus genotypes, both wild-relative species and cultivated hybrid rootstocks, were subjected to leaf ash and carbon isotope discrimination (Δ13C) analyses, which are strongly correlated to water use efficiency (WUE). Almond and peach wild relative species showed the lowest Δ13C ratios, and therefore, the highest WUE in comparison with hybrid genotypes. In addition, drought-related cis-regulatory elements (CREs) were identified in the promoter regions of the effector gene PpDhn2, and the transcription factor gene DREB2B, two genes involved in drought-response signaling pathways. The phylogenetic analysis of these regions revealed variability in the promoter region sequences of both genes. This finding provides evidence of genetic diversity between the peach- and almond-relative individuals. The results presented here can be used to select Prunus genotypes with the best drought resistance potential for breeding. Full article
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Review

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Open AccessReview Plant Desiccation Tolerance and its Regulation in the Foliage of Resurrection “Flowering-Plant” Species
Agronomy 2018, 8(8), 146; https://doi.org/10.3390/agronomy8080146
Received: 29 June 2018 / Revised: 7 August 2018 / Accepted: 9 August 2018 / Published: 14 August 2018
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Abstract
The majority of flowering-plant species can survive complete air-dryness in their seed and/or pollen. Relatively few species (‘resurrection plants’) express this desiccation tolerance in their foliage. Knowledge of the regulation of desiccation tolerance in resurrection plant foliage is reviewed. Elucidation of the regulatory
[...] Read more.
The majority of flowering-plant species can survive complete air-dryness in their seed and/or pollen. Relatively few species (‘resurrection plants’) express this desiccation tolerance in their foliage. Knowledge of the regulation of desiccation tolerance in resurrection plant foliage is reviewed. Elucidation of the regulatory mechanism in resurrection grasses may lead to identification of genes that can improve stress tolerance and yield of major crop species. Well-hydrated leaves of resurrection plants are desiccation-sensitive and the leaves become desiccation tolerant as they are drying. Such drought-induction of desiccation tolerance involves changes in gene-expression causing extensive changes in the complement of proteins and the transition to a highly-stable quiescent state lasting months to years. These changes in gene-expression are regulated by several interacting phytohormones, of which drought-induced abscisic acid (ABA) is particularly important in some species. Treatment with only ABA induces desiccation tolerance in vegetative tissue of Borya constricta Churchill. and Craterostigma plantagineum Hochstetter. but not in the resurrection grass Sporobolus stapfianus Gandoger. Suppression of drought-induced senescence is also important for survival of drying. Further research is needed on the triggering of the induction of desiccation tolerance, on the transition between phases of protein synthesis and on the role of the phytohormone, strigolactone and other potential xylem-messengers during drying and rehydration. Full article
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Open AccessReview Profiling of the Differential Abundance of Drought and Salt Stress-Responsive MicroRNAs Across Grass Crop and Genetic Model Plant Species
Agronomy 2018, 8(7), 118; https://doi.org/10.3390/agronomy8070118
Received: 21 May 2018 / Revised: 6 July 2018 / Accepted: 10 July 2018 / Published: 13 July 2018
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Abstract
In recent years, it has become readily accepted among interdisciplinary agriculturalists that the current global crop yield to land capability ratio is significantly insufficient to achieve food security for the predicted population of 9.5 billion individuals by the year 2050. This issue is
[...] Read more.
In recent years, it has become readily accepted among interdisciplinary agriculturalists that the current global crop yield to land capability ratio is significantly insufficient to achieve food security for the predicted population of 9.5 billion individuals by the year 2050. This issue is further compounded by the: (1) food versus biofuel debate; (2) decreasing availability of arable land; (3) required reductions to the extensive and ongoing environmental damage caused by either poor agricultural practices or agriculture expansion, and; (4) increasingly unfavorable (duration and severity) crop cultivation conditions that accompany man-made climate change, driven by ever-expanding urbanization and its associated industrial practices. Mounting studies are repeatedly highlighting the critical importance of linking genotypes to agronomically beneficial phenotypes and/or using a molecular approach to help address this global crisis, as “simply” clearing the remaining natural ecosystems of the globe for the cultivation of additional, non-modified crops is not efficient, nor is this practice sustainable. The majority of global food crop production is sourced from a small number of members of the Poaceae family of grasses, namely; maize (Zea mays L.), wheat (Triticum aestivum L.) and rice (Oryza sativa L.). It is, therefore, of significant concern that all three of these Poaceae grass species are susceptible to a range of abiotic stresses, including drought and salt stress. Highly conserved among monocotyledonous and dicotyledonous plant species, microRNAs (miRNAs) are now well-established master regulators of gene expression, influencing all aspects of plant development, mediating defense responses against pathogens and adaptation to environmental stress. Here we investigate the variation in the abundance profiles of six known abiotic stress-responsive miRNAs, following exposure to salt and drought stress across these three key Poaceae grass crop species as well as to compare these profiles to those obtained from the well-established genetic model plant species, Arabidopsis thaliana (L.) Heynh. Additionally, we outline the variables that are the most likely primary contributors to instances of differential miRNA abundance across the assessed species following drought or salt stress exposure, specifically; (1) identifying variations in the experimental conditions and/or methodology used to assess miRNA abundance, and; (2) the distribution of regulatory transcription factor binding sites within the putative promoter region of a MICRORNA (MIR) gene that encodes the highly conserved, stress-responsive miRNA. We also discuss the emerging role that non-conserved, species-specific miRNAs play in mediating a plant’s response to drought or salt stress. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Sugar Transporters Expression in Response to Drought and Salt Stress

Nils Hennion, Laurence Maurousset, Nathalie Pourtau, and Lemoine Rémi *

Team Sugar and Exchange Plant-Environment, UMR Université de Poitiers/CNRS 7267 Ecology and Biology of Interactions, Bâtiment B31,3, rue Jacques Fort TSA 51106 86073 POITIERS CEDEX 9, France

* Correspondance: remi.lemoine@univ-poitiers.fr; Tel : +33-549-914-185

Plant development and crop yield are highly affected by drought and salt stress. At the physiological level, both stresses are characterized by a deficit in water available to cells with the added toxicity of sodium in the case of salt stress. Efficient source to sink transport of sugars via the phloem is an important determinant of plant productivity and is partly regulated by specific membrane transporters located at strategic location inside and outside the phloem. Transport of sugars is sensitive to environmental clues (Lemoine et al., 2013, Frontiers in Plant Science, 4) and manipulating it to provide tolerance to drought and salt stress is highly relevant. The main raisons are that sugars and sugar alcohols are involved in osmotic response of cells and that sugar distribution between source and harvestable sink has to be maintained during stress. In this review, we will focus on the regulation of genes coding for enzymes involved in sugar (sucrose, hexose, sugar alcohols, trehalose…) metabolism and transport as potential targets to improve drought and salt stress tolerance in crops, taking advantage of the data obtained in the model plant Arabidopsis.

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